1. Field of the Invention
This invention relates to battery testers and, more particularly, to battery testers which can determine the deteriorated state of a battery from simultaneous measurements of the internal resistance, terminal voltage, etc. of the battery.
2. Description of the Prior Art
The deteriorated state of a battery (either primary or secondary battery) is usually determined from the internal resistance (or equivalent series resistance) and terminal voltage of the battery. Battery deterioration tends to result in internal resistance increase and terminal voltage reduction of the battery.
Heretofore, the deteriorated state of a battery is determined by using an AC resistance gauge (for instance AC m .OMEGA. gauge) and a tester (or circuit tester). The internal resistance of the battery is measured with the AC resistance gauge, and the terminal voltage is measured with the tester. According to these measurements the deteriorated state of the battery can be determined. The internal resistance of the battery is temperature-dependent, and when more accurate judgment is required, the ambient temperature around a part of the battery under measurement is measured with a temperature gauge, and taken into consideration as reference data for the battery deterioration judgment.
This battery deterioration judgment, however, requires two measuring instruments, i.e., the AC resistance gauge and the tester. In addition, the internal resistance and the terminal voltage have to be measured separately, and these measuring operations are inevitably cumbersome. Moreover, in the case of taking the ambient temperature into consideration AS reference data, the temperature measurement with a temperature gauge is necessary and increases the operational burden.
Further cumbersomeness is added to the battery deterioration judgment on the bases of the above measurements by different criteria of judgment with different battery manufacturers and models. In other words, whenever battery deterioration judgment is made, it is necessary to make cumbersome checks of battery characteristics from battery specifications or the like.
As an example, a case of measuring the internal resistance of a vehicle-mounted battery will now be described. As shown in FIG. 10, a pair of source side probes 1a and 1b led out from an AC constant-current generator 1, and a pair of sense side probes 2a and 2b from an AC volt meter 2, are held in contact with the plus and minus terminals, respectively, of a battery BT. An AC current for measurement is caused from the AC current generator 1, and the terminal voltage generated across the battery BT is measured with the AC volt meter 2. The measurement is converted in a next stage A/D converter into digital data, which is in turn converted in a CPU 4 into a corresponding resistance.
When the internal resistance Rs of the battery is increased due to deterioration thereof or like cause, the terminal voltage generated across the battery is correspondingly increased. When a rating value of measurement is exceeded, overflow of the A/D converter 3 takes place.
In the principle underlying the above measurement, the source side pair probes 1a and 1b and sense side pair probes 2a and 2b, i.e., a total of four probes, are electrically connected to the plus and minus terminals of the battery BT. However, independently connecting the probes to the terminals is time-consuming. Actually, therefore, one source side probe 1a and one sense side probe 2a are commonly connected to a positive side clamp probe of a clip type, while commonly connecting the other source side probe 1b and the other sense side probe 2b to a negative side clamp probe of like type, and then the two, i.e., positive and negative side clamp probes, are connected to the plus and minus terminals, respectively, of the battery BT.
Where the above clamp probes are used as two terminals, however, in the event of defective connection between the clamp probes and battery terminals or breaking due to detachment of the clamp probes from the battery terminals, the AC constant-current generator 1 is brought to a load-free state, and its output voltage is directly applied across the AC volt meter 2. Therefore, the overflow of the A/D converter 3 takes place due to the reason noted above.
A problem is therefore posed that it cannot be determined whether overflow of the A/D converter 3 is caused by battery internal resistance increase or by defective contact (or breaking) of the clamp probes with respect to the battery terminals.
In the case of directly using the four probes 1a, 1b, 2a and 2b as respective terminals as shown in FIG. 10, without replacing these probes with the two clamp probes, a resistor with a high resistance is sometimes connected between the probes 1a and 2a to prevent the open circuit therebetween. Again in such a case, defective contact regarded to be a breaking between these probes and the battery terminals would result in overflow of the A/D converter 3.